Passengers get off the N Judah line at Cole St. and Carl St. in San Francisco, Calif., Tuesday, May 22, 2012. The line is shutting down for nine days starting Friday.

Photo: Sarah Rice, Special To The Chronicle

Passengers get off the N Judah line at Cole St. and Carl St. in San...

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The N Judah line runs on Irving St. in San Francisco, Calif., Tuesday, May 22, 2012. The line is shutting down for nine days starting Friday.

Photo: Sarah Rice, Special To The Chronicle

The N Judah line runs on Irving St. in San Francisco, Calif.,...

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A sign in the bus stop at Cole St. and Carl St. in San Francisco, Calif., Tuesday, May 22, 2012, lets riders know the construction won't close businesses. The N Judah line is shutting down for nine days starting Friday.

Photo: Sarah Rice, Special To The Chronicle

A sign in the bus stop at Cole St. and Carl St. in San Francisco,...

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Passengers get off the N Judah line at Cole St. and Carl St. in San Francisco, Calif., Tuesday, May 22, 2012. The line is shutting down for nine days starting Friday.

Photo: Sarah Rice, Special To The Chronicle

Passengers get off the N Judah line at Cole St. and Carl St. in San...

Image 5 of 5

A sign at Cole St. and Carl St. shows riders where the temporary stop will be when the N Judah line shuts down for nine days starting Friday.

For nine days beginning Friday night, Muni's busiest line - the N-Judah - will shut down while a well-worn stretch of rail is replaced. The Metro line's nearly 40,000 daily passengers, already accustomed to crowded commutes, will have to pack onto buses or find another way to get downtown and back.

"It's only a week and a half," said Jennie Hinchcliff, a 39-year-old college professor, "but I'm sure it will seem longer."

The N-Judah runs from Ocean Beach through the Sunset District and the Haight, downtown in the Market Street subway and along the Embarcadero to the Caltrain station at Fourth and King streets. On weekdays, it hauls about 30 percent of the passengers on Muni's six Metro rail lines.

The Municipal Transportation Agency plans to run shuttles along the route, but buses can't haul all of the N-Judah passengers. And they won't make the trip as quickly because they can't travel through the subway and will have to creep through traffic.

"We're encouraging people to walk, ride a bike or stay home if they can," said Paul Rose, Muni spokesman. "We want to make as much room as possible on the shuttles."

Muni's light-rail vehicles can hold up to 200 passengers per single-car train, Rose said, while the agency's articulated buses only carry 80.

"We're just trying to make it as painless as possible for people," he said.

To make things even more challenging, the rail work will also force the J-Church, which hauls about 14,000 riders each weekday, to curtail its route at Church and Market streets, where passengers can transfer at Church Street station to other Metro lines running in the subway.

Rerouted bus lines

The 22-Fillmore, 37-Corbett, 43-Masonic and N-Owl buses will be rerouted around the construction zone in the area around the Church Street and Duboce Avenue intersection.

With the intersection shut down, crews will work around the clock to replace a critical stretch of rail, build new boarding areas and make repairs to the streets, sidewalks, sewers and water systems. The rail work is part of an ongoing program to ensure the Muni system is safe and in good repair; the other work is taking advantage of the shutdown to make improvements.

Work on the N-Judah, which included earlier, but shorter, shutdowns at Church and Duboce and Carl and Cole streets, is part of a $40.6 million effort that started in spring of 2011. The agency is in the midst of a multiyear, $141 million rail-replacement project involving several Muni Metro lines.

Holiday weekend

Rose said the agency chose this week for the long shutdown because it anticipates lower-than-average ridership over Memorial Day weekend and the following week. The shutdown starts at 7 p.m. Friday and is expected to continue through 5 a.m. June 4. Muni has been warning passengers with signs on trains and in stations. During the shutdown, it will have ambassadors stationed at busy boarding zones to help direct riders.

When the work is done, Rose said, passengers will enjoy "a smoother and faster ride."

Passengers aboard the N-Judah Tuesday afternoon said they were dreading life without the Metro trains.

"I'm not at all prepared for it," said Anthony Cabrera, 38, sitting in front of a "Countdown to Shutdown" sign. "I work at Trader Joe's at Ninth and Bryant and I depend on this train to get to work."

He'll brave the shuttle buses, he said, but says Muni "should have made better accommodations" for regular riders.

"I think it's going to be a madhouse. People will be pushing and shoving. There's going to be a lot of pissed-off people - and I'll be one of them."

Encourages bike riding

Hinchcliff said the shutdown would probably encourage her to ride her bike and walk more and do more shopping and dining in her neighborhood instead of heading downtown. But she'll still have to hop the shuttles to get to the Academy of Art University, where she teaches fine arts.

"Whenever they run shuttles, it's less than ideal," she said. "I'm not looking forward to it. I think it's going to be kind of crazy."

Detours

The N-Judah will be closed from 7 p.m. Friday through 5 a.m. June 4. For more information, visit the Municipal Transportation Agency website at www.sfmta.com.